Advances in microelectronics technology have resulted in electronic devices that process signals and data at unprecedented high speeds. Electronic and/or integrated circuit (“IC”) devices, e.g., microprocessors, memory devices, etc, become smaller while heat dissipation requirements get larger. Thermal materials have been used in packaging as interfaces between devices to dissipate heat from these devices (e.g., microprocessors). One typical thermal interface material (TIM) typically includes a polymer matrix and a thermally conductive filler. The TIM technologies used for electronic packages encompass several classes of materials such as phase change materials, epoxies, greases, and gels.
Boron nitride (BN) is a chemically inert non-oxide ceramic material which has a multiplicity of uses based upon its electrical insulating property, corrosion resistance, high thermal conductivity and lubricity. As illustrated in FIG. 1, thermal conductivity along the x-y plane of a boron nitride platelet is greater than through the thickness (z-direction) of the platelet. Thermal conductivity of the z-direction of the boron nitride hexagonal crystal structure is 2.0 W/mK, while the thermal conductivity in the x-y plane is 400 W/mK, as described in “Characterization and Performance of Thermally Conductive Epoxy Compound Fillers”, R. F. Hill, SMTA National Symposium “Emerging Packaging Technologies”, Research Triangle Park, N.C., Nov. 18-21, 1996. BN platelets have a thermal conductivity of 59 W/mK in the direction parallel to the pressing direction and 33 W/mK in the direction perpendicular to the pressing direction (as measured in hot pressed BN shapes of approximately 90 to 95% of theoretical density). A preferred use for BN is as a filler material additive to a polymeric compound, for use in a thermal interface application.
US Patent Publication No. 2004-0077764 discloses a thermal interface material composed of a polymer selected from the group consisting of a polyester, epoxy or polyamide and spherical agglomerate particles of BN loaded to a concentration of between 30-50 wt. % BN. As disclosed in US 2006-0127422, thermal interface materials comprising these spherical BN particles have a thermal conductivity ranging from 1 W/mK to about 40 W/mK. When platelet-shaped hBN particles, i.e., less expensive BN powder not in spherical agglomerate form, are used in thermal interface materials at a similar loading (and depending on the polymer matrix used), one typically obtains a maximum through-plane thermal conductivity (TC) in the range 0.3-6 W/mK. U.S. Pat. No. 6,919,504 discloses a flexible heat sink article comprising a base comprising a polymer and a plurality of polymeric protrusions, wherein the protrusions comprise non-spherical thermally conductive particles substantially aligned in the direction of the major dimension within the protrusions.
There is still a need for thermal interface materials and methods for making thermal interface materials having improved thermal conductivity property by maximizing the anisotropic benefit of boron nitride to the fullest extent.